This invention relates to improved surfactant compositions.
Alkylbenzene sulfonates, the sulfonated derivatives of alkylbenzenes, are known surfactants commonly used in a variety of applications where surfactants are required (detergents, hard-surface cleaners, drilling fluids, cutting fluids, etc.). An alkylbenzene molecule includes an acyclic aliphatic alkyl chain, typically produced by distilling a boiling range fraction of hydrocarbons from a petroleum based feedstock. This boiling range fraction typically contains mostly hydrocarbons having between 10 and 13 carbon atoms per molecule (C10-C13 hydrocarbons). This alkyl chain is typically dehydrogenated and alkylated with benzene to form alkylbenzene, the hydrophobic portion of the alkylbenzenesulfonate molecule. The alkylbenzene molecule is further derivatized, typically via sulfonation with sulfur trioxde, to produce the alkylbenzenesulfonate, where the sulfonate group is attached to the benzene portion of the alkylbenzene, and is the hydrophilic portion of the surfactant molecule.
Historically, highly branched alkylbenzenesulfonate (ABS) surfactants were used in detergents. However, these were found to be poorly biodegradable and were replaced by linear alkylbenzenesulfonates (LAS), which are readily biodegradable. Further improvements to LAS include the production of “modified LAS”, or “MLAS” (MLAS), which consists of 2 modifications to the LAS molecule: a higher concentration of the 2-phenyl isomer, which improves surface activity, and the introduction of a limited amount of methyl-branching in the alkyl chain, which improve solubility.
Although typical alkylbenzenesulfonates are popular due to their availability and excellent cost/performance attributes, they are prone to interaction with hard-water ions (calcium & magnesium ions), which effectively reduces their solubility, and therefore their ability to act as surface active agents. Colder temperatures exacerbate this effect. Even C10-13 MLAS, although improved in terms of surface activity and solubility, is negatively impacted by water hardness ions and/or colder water temperatures.
In order to evaluate the effectiveness of surfactant or detergent compositions, it would therefore be important to measure various performance parameters such as intrinsic detergency performance (cleaning ability), Ca2+ (water hardness) tolerance, surface activity, salt (NaCl) tolerance and cold water detergency performance.
A test of Intrinsic Detergency gives an indication of a surfactant's cleaning ability, and is therefore a test of detergency performance. The Ca2+ tolerance/turbidity measurement provides information on the level of soluble surfactant available for interfacial activity in dependence of the water hardness. With increasing water hardness (increasing amounts of calcium ions) the solubility of LAS type surfactants usually decreases; the surfactant starts to precipitate and the solution becomes turbid.
In order to evaluate the interfacial activity of a surfactant composition, the surface tension of surfactant compositions can be determined in dependence of the water hardness. This measurement determines the optimum solubility conditions for the given surfactant in order to maximize interfacial activity.
The dynamic surface tension measurement is the determination of the surface tension (or interfacial activity) in dependence of the surface age. Especially for dynamic processes like washing and cleaning the dynamic properties of a surfactant are even more important than the static ones.
Salt (NaCl) tolerance is determined by measuring solubility of the surfactant in solutions of high ionic strength. The measurement of the transparency of the solution gives an indication of the surfactant's solubility at a specific salt concentration. High salt tolerance would be important for technical applications where high salt loads are found. Examples include enhanced oil recovery (EOR), emulsion polymerization or metal working fluids.
Lastly, it would also be important to evaluate a surfactant's cold water detergency performance by determining its ability to remove solid soil under cold water conditions.
It is an object of this invention to provide new surfactant compositions that, apart from being readily biodegradable, soluble and having good surface activity, have significantly improved hard water tolerance, good physical application (washing) properties at higher water hardness and low temperature conditions, and have excellent tolerance to ionic strength.